The syndecans are a family of transmembrane heparan sulfate proteoglycans defined (i) by highly conserved cytoplasmic domains and (ii) ectodomains that are divergent but bear heparan sulfate. Their function is mediated by heparan sulfate chain binding a variety of matrix and growth factor ligands and the conserved but unidentified role of the cytoplasmic domain Syndecan-1 is regulated during the development of epithelial organs at the level of protein translation, apparently correlating with regulated binding of an unidentified phosphoprotein. When expressed, it is required for the calcium-dependent adhesion that maintains the epithelial morphology. The object of this proposal is to study these two regulatory mechanisms by defining (i) the structure(s) within the syndecan-1 mRNA that controls its utilization and (ii) structures within the transmembrane and cytoplasmic domain of the core protein that function in the acquisition and/or maintenance of epithelial morphology. This study will use molecular techniques to generate truncations and deletions within the mouse syndecan-1 cDNA that will mutate the 5' UTR of transcribed mRNAs or mutate functional domains within the syndecan-1 core protein. Messenger RNA utilization will be correlated with regulatory phosphoprotein binding either in 172 vitro translation systems, or in transfected cells. The latter will employ elicited mouse macrophages, in which the translational block is operative, but is overcome by elevated cytoplasmic cAMP. The function of core protein mutations will be examined by transfection into three complementary study systems: Raji lymphoblastoid cells will be examined for the acquisition of spreading on syndecan-1 specific probes; NMuMG mammary epithelial cells will be examined for blockage of endogenous syndecan-1 function; S115 mammary carcinoma cells, which become metastatic without functional syndecan-l, will be assessed for maintenance of normal epithelial morphology by the mutants. The activity of the core protein mutations will be correlated with cytoskeleton binding and phosphorylation of the cytoplasmic domain. The proposed study will provide understanding of the role of syndecan-1 regulation in controlling the epithelial growth and morphogenesis that accompanies formation of human epithelial organs and growth/involution of human mammary glands. The insight derived will provide cures for defects that lead to malignant carcinomas and birth defects.